• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.58-59
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• 2006

Less than a decade ago, most alternate membrane materials for fuel cells relied upon a post-sulfonation process to generate ionic groups capable of transporting protons from the anode to the cathode. These random post sulfonations showed some promise, but in general they produced materials that were not sufficiently stable or protonically conductive at ion exchange capacities where aqueous swelling could be restricted. Our group began to synthesize disulfonated monomers that could be used to incorporate into random copolymer proton exchange membranes. The expected limitation was that the aromatic polymers might not be stable enough to withstand fuel cell conditions. However, this was mostly based upon an accelerated test known was the Fenton's Reagent Test, which did not seem to this author as being a reliable predictor of performance. A much better approach has been to evaluate the open circuit voltage (OCV) for alternate membranes, as well as the benchmark perfluorosulfonic acid systems. When this is done, the aromatic ionomers of this study, primarily based upon disulfonated polyarylene ether sulfones, show up quite well. Real time 3000 hours DMFC results have also been generated. Obtaining conductive materials at low humidities is another major issue where alternate membranes have not been particularly successful. In order to address this problem, multiblock copolymers with relatively high water diffusion coefficients have been designed, which show promise for conductivity at lowered humidity.

• Journal of Communications and Networks
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• 제14권4호
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• pp.396-409
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• 2012

With the proliferation of diverse wireless devices, there is an increasing concern about the security of location information which can be spoofed or disrupted by adversaries. This paper investigates the characterization and detection of location spoofing attacks, specifically those which are attempting to falsify (degrade) the position estimate through signal strength based attacks. Since the physical-layer approach identifies and assesses the security risk of position information based solely on using received signal strength (RSS), it is applicable to nearly any practical wireless network. In this paper, we characterize the impact of signal strength and beamforming attacks on range estimates and the resulting position estimate. It is shown that such attacks can be characterized by a scaling factor that biases the individual range estimators either uniformly or selectively. We then identify the more severe types of attacks, and develop an attack detection approach which does not rely on a priori knowledge (either statistical or environmental). The resulting approach, which exploits the dissimilar behavior of two RSS-based estimators when under attack, is shown to be effective at detecting both types of attacks with the detection rate increasing with the severity of the induced location error.

• Fibers and Polymers
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• 제2권4호
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• pp.196-202
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• 2001

In order to investigate the relationship between subjective sensation for fabric sound and touch and the objective measurements, eight different apparel fabrics were selected as specimens. Sound parameters of fabrics including level pressure of total sound (LPT), level range (ΔL), and frequency differences (Δf) and mechanical properties by Kawabata Evaluation System (KES) were obtained. For subjective evaluation, seven aspects of the sound (softness, loudness, pleasantness, sharpness, clearness, roughness, and highness) and eight of the tough (hardness, smoothness, fineness, coolness, pliability, crispness, heaviness, and thickness) were rated using semantic differential scale. Polyester ultrasuede was evaluated to sound softer and more pleasant while polyester taffeta to sound louder and rougher than any other fabrics. Wool fabric such as worsted and woolen showed similar sensation for sound but differed in some touch sensation in that woolen was coarseast, heaviest, and thickest in touch. In the prediction model for sound sensation, LPT affected positively subjective roughness and highness as well as loudness, while ΔL was found as a parameter related positively with softness and pleasantness. Touch sensation was explained by some of mechanical properties such as surface, compressional, shear, and bending properties implying that a touch sensation could be expressed by a variety of properties.

• Advances in aircraft and spacecraft science
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• 제4권4호
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• pp.467-486
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• 2017

A method for decoupling reliability based design optimization problem into a set of deterministic optimization and performing a reliability analysis is described. The inner reliability analysis and the outer optimization are performed separately in a sequential manner. Since the outer optimizer must perform a large number of iterations to find the optimized shape and size of structure, the computational cost is very high. Therefore, during the course of this research, new multilevel reliability optimization methods are developed that divide the design domain into two sub-spaces to be employed in an iterative procedure: one of the shape design variables, and the other of the size design variables. In each iteration, the probability constraints are converted into equivalent deterministic constraints using reliability analysis and then implemented in the deterministic optimization problem. The framework is first tested on a short column with cross-sectional properties as design variables, the applied loads and the yield stress as random variables. In addition, two cases of curvilinearly stiffened panels subjected to uniform shear and compression in-plane loads, and two cases of curvilinearly stiffened panels subjected to shear and compression loads that vary in linear and quadratic manner are presented.

• Steel and Composite Structures
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• 제36권3호
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• pp.339-353
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• 2020

This study investigates the seismic performance of steel reinforced concrete (SRC) T-shaped columns under low cyclic loading tests. Based on test results of ten half-scale column specimens, failure patterns, hysteretic behavior, skeleton curves, ultimate strength, ductility, stiffness degradation and energy dissipation capacity were analyzed. The main variables included loading angles, axial compression ratios and steel ratios. The test results show that the average values of the ductility factor and the equivalent viscous damping coefficient with respect to the failure of the columns were 5.23 and 0.373, respectively, reflecting good seismic performance. The ductility decreased and the initial stiffness increased as the axial compression ratio of the columns increased. The strength increased with increasing steel ratio, as expected. The columns displaced along the web had higher strength and initial stiffness, while the columns displaced along the flange had better ductility and energy dissipation capacity. Based on the test and analysis results, a formula is proposed to calculate the effective stiffness of SRC T-shaped columns.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.240-247
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• 2006

Piezoelectric sensor-based health monitoring technique using a two-step support vector machine (SYM) classifier is discussed for damage identification of a railroad track. An active sensing system composed of two PZT patches was investigated in conjunction with both impedance and guided wave propagation methods to detect two kinds of damage of the railroad track (one is a hole damage of 0.5cm in diameter at web section and the other is a transverse cut damage of 7.5cm in length and 0.5cm in depth at head section). Two damage-sensitive features were extracted one by one from each method; a) feature I: root mean square deviations (RMSD) of impedance signatures and b) feature II: wavelet coefficients for $A_0$ mode of guided waves. By defining damage indices from those damage-sensitive features, a two-dimensional damage feature (2-D DF) space was made. In order to minimize a false-positive indication of the current active sensing system, a two-step SYM classifier was applied to the 2-D DF space. As a result, optimal separable hyper-planes were successfully established by the two-step SYM classifier: Damage detection was accomplished by the first step-SYM, and damage classification was also carried out by the second step-SYM. Finally, the applicability of the proposed two-step SYM classifier has been verified by thirty test patterns.

• Journal of Forest and Environmental Science
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• 제31권4호
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• pp.288-296
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• 2015

In many very high density cities in Asia in which there is limited area to expand, growth is forced upward as well as outward. Densely packed detached houses and low-rise buildings are replaced by lower density high-rises, leaving open spaces between high-rise buildings. Through this process, areas that formerly did not have much green space gain valuable green spaces, and new ecological corridors and patches are created. In this study, the demographic and housing-type changes of Wonju City were delineated using land use maps, aerial images, census data, and other administrative data. Green area changes were calculated using land cover data derived from multi-year Landsat TM satellite imagery. The values were then compared against demographic and housing-type changes for each administrative unit. The overall results showed a decrease of forested area in the city and an increase of developed area. Urban sprawl was clearly visible in many of the suburban areas. However, as expected, we also detected areas in which greenness did not decrease when the population greatly increased. These areas were characterized by residential building complexes of ten or more stories. If an equal number of housing units had been built as detached houses, these areas would not have kept as much green space. Our research result showed that high-density and high-rise residential structures can offer an alternative means to protect or create urban green spaces in high-density urban environments.

• Advances in concrete construction
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• 제9권4호
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• pp.367-374
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• 2020

Concrete surfaces, industrial floors, sidewalks, roads and parking lots are typically subjected to abrasions. Many studies indicated that the abrasion resistance is directly related to the ultimate strength of the cured concrete. Chemical reactions, freeze-thaw cycles, and damages under abrasion are among many factors negatively affecting the concrete strength and durability. One of the major solutions to address the abrasive resistance of the concrete is to use fibers. Fibers are used in the concrete mix to improve the mechanical properties, strength and limit the crack propagations. In this study, implementation of the steel fibers in concrete to enhance the abrasive resistance of the concrete is investigated in details. The abrasive resistance of the concrete with and without steel fibers is studied with the sandblasting technique. For this purpose, different concrete samples are made with various hooked steel fiber ratios and investigated with the sandblasting method for two different strike angles. In total, 144 ASTM verified cube samples are investigated and it is shown that those samples with the highest steel fiber ratios have the highest abrasive resistance. In addition, the experiments determine that there is a meaningful correlation between the steel fiber percentage in the mix, strike angle and curing time which could be considered for improving structural behavior of the fiber-reinforced concrete.

• Management Science and Financial Engineering
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• 제15권1호
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• pp.51-69
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• 2009

A network model and a Genetic Algorithm (GA) is proposed to solve the simultaneous estimation of the trip distribution and traffic assignment from traffic counts in the congested networks in a logit-based Stochastic User Equilibrium (SUE). The model is formulated as a problem of minimizing a non-linear objective function with the linear constraints. In the model, the flow-conservation constraints are utilized to restrict the solution space and to force the link flows become consistent to the traffic counts. The objective of the model is to minimize the discrepancies between two sets of link flows. One is the set of link flows satisfying the constraints of flow-conservation, trip production from origin, trip attraction to destination and traffic counts at observed links. The other is the set of link flows those are estimated through the trip distribution and traffic assignment using the path flow estimator in the logit-based SUE. In the proposed GA, a chromosome is defined as a real vector representing a set of Origin-Destination Matrix (ODM), link flows and route-choice dispersion coefficient. Each chromosome is evaluated by the corresponding discrepancies. The population of the chromosome is evolved by the concurrent simplex crossover and random mutation. To maintain the feasibility of solutions, a bounded vector shipment technique is used during the crossover and mutation.

• 유통과학연구
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• 제16권8호
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• pp.15-27
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• 2018

Purpose - The purpose of the study is to examine the relationships among the following retail operations variables: retail store operations (i.e., store management, sales personnel, promotion of merchandise), success of assortment planning, firm performance (i.e., market share, overall competitive position, profitability, product quality, consumer satisfaction), and retail buyer's demographics and firm's characteristics. Research design, data, and methodology - After conducting a pilot test, the survey was conducted in Seoul, South Korea. With using the listwise deletion method, 378 usable data sets were analyzed. For data analysis, descriptive statistics, factor analysis, and Structural Equation Modeling (SEM) methods were employed. Results - As evidenced from the path diagram, the relationship between retail store operations and the success of assortment planning is strong and significant. Retail store operations affect firm performance, though at a weaker significance than it affects the success of assortment planning. The relationship between the success of assortment planning and firm performance, is the strongest relationship observed by this research. Conclusions - The findings of this empirical study contribute to the retail/fashion buying/management field by confirming (a) the importance of assortment planning for retail firm performance and (b) the role of store operations for successful assortment planning and firm performance for fashion retailers.